A Compact Type a Inclusion with Multiple Wark-lovering Rims: a Complex History Recorded in Pyroxene

Introduction. The Wark-Lovering rims [1] found on many refractory inclusions are important recorders of nebular environments to which refractory inclusions were exposed after their formation, such as different temperature regimes and isotopic reservoirs [2]. As part of a large-scale survey of W-L rims to enable us to better understand the range of environments reflected in rims, an inclusion of interest was found in Leoville, a member of the reduced CV3 subgroup. This inclusion may have four generations of rims and six texturally and chemically distinct occurrences of pyroxene. Methods. Two polished sections of L6, a compact Type A (CTA) inclusion, were examined with the scanning electron microscope. Backscattered electron images and elemental X-ray maps of selected areas were collected. Electron probe analyses were collected in linear traverses across layers and at selected spots. Observations and Results. One section sampled the interior of the inclusion and has spinel (typically euhedral, 50 μm across) clusters and isolated fassaite grains (anhedral, ~500 μm across) enclosed in unaltered melilite (Åk3-30) with sparse, isolated perovskite grains throughout. The other section, which sampled the interior and the outer margin of the inclusion, shows that spinel is concentrated toward the edge of the inclusion in a discontinuous layer with a thickness up to 100 μm, intergrown with melilite. Outside of the spinel layer there are occurrences of pyroxene±melilite. This report focuses on three of these occurrences: Rim Area 4 (RA4), RA5 and RA6. The most complex of these is RA5, shown in Fig. 1. In this view the interior of the inclusion is toward the top of the image; meteorite matrix (Mtx) is visible at the bottom-center (bright material). From the inclusion interior outward there is a spinel-rich layer; a thin layer of pyroxene with >12 wt% Ti as TiO2, (“Ti-rich pyx” in Fig. 1); a thicker layer of pyroxene (dark band labeled “Ti-poor pyx” in Fig. 1); a thick zone of melilite (Åk220) + spinel + perovskite; and an outermost rim layer of very Ti-poor, Si-rich pyx (diopside). RA4 (Fig. 2) is best described as a “peninsula” of mel + spinel that projects outward from the inclusion into the matrix (toward the lower right corner of Fig. 2). At its contact with the inclusion interior is a layer of spinel and one of Ti-rich pyx. An outer diopside rim unconformably contacts and overlies one end of the Ti-rich pyx layer and wraps around the peninsula. RA6 has a fine intergrowth of Ti-rich pyx and spinel and an outer rim of diopside. Fig. 1. Backscattered electron (BSE) image of RA5 showing three occurrences of pyroxene (pyx).